Formulation and production of personal care products, such as shampoos, conditioners, depilatories, sunscreens and the like, presents a number of challenges. Some ingredients used in such products may contribute to skin and eye irritation. For example, shampoos usually include various surface-active compounds or surfactants, depilatories are formulated with organic or inorganic bases, and certain skin care preparations contain hydroxy acids, all of which may cause irritation. Additionally, certain products (e.g., soaps, detergents, cleansers, shaving creams, etc.) may remove some of the skin's protective lipids and thus increase skin's sensitivity to other formulation components, which might otherwise not produce irritation.
Whatever the cause of the irritation, many attempts have been made to reduce the irritation potential of personal care and cosmetic products by identifying ingredients that cause irritation, and reducing the concentration(s) of such ingredients or eliminating them entirely. However, in many cases, it may not be practical or desirable to reduce or eliminate the irritating ingredient, which is often the active ingredient of the formulation. For example, surfactants, bases, and hydroxy acids are included in shampoos, depilatories, and certain skin care products, respectively, to achieve the primary purpose of the product formulation. Therefore, instead of removing the irritants, it may be desirable to include anti-irritating compounds in the cosmetic and personal care formulations.
The use of anti-irritants in cosmetics had been suggested, for example, in articles by R. L. Goldemberg, Use of Anti-Irritants in Cosmetic Formulating, J. Soc. Cosmetic Chemists, 6: 317–340 (1965), and Anti-irritants, J. Soc. Cosmetic Chemists, 30:415–427 (1979), which are incorporated herein by reference. Goldemberg defined an anti-irritant as any agent “which when used in conjunction with skin or eye irritants, reduces their irritation sufficiently to be tolerated when applied to the body.” A broader definition would consider a compound anti-irritating if it reduces irritation of the human body to any degree when used in combination with an irritant relative to the use of the same irritant, under the same conditions, without the anti-irritant.
In other words, a compound is generally considered anti-irritating if it reduces irritation when applied in a formulation with an irritant. Under this definition, any material that is applied separately from the irritating components of a product, e.g., before the product is applied, is generally not considered an anti-irritant. For example, there exists a known practice of applying a layer of petrolatum to the scalp before using a high-pH relaxer. Even though petrolatum does reduce scalp irritation by the relaxer, it would not be an anti-irritant because it is applied separately, unless petrolatum also reduces irritation when applied in a formulation with the relaxer.
Several mechanisms of anti-irritation activity had been suggested. One proposed mechanism involves a reduction in the irritating ability of the irritant by a complexation of the irritant with the anti-irritating compound. Polyvinyl pyrrolidone (PVP), which is known to reduce the irritating ability of iodine, is an example of anti-irritants that are believed to operate via this mechanism. When PVP is added to a solution of iodine, the latter no longer irritates mucousal tissue while retaining its germicidal activity.
Another suggested mechanism is blocking of chemically reactive sites of skin keratin by the anti-irritant, which thus prevents the irritant from accessing the reactive sites. For example, polyquaternium-10 and stearyl dimethylamine oxide are thought to operate by this mechanism.
Yet another suggested mechanism is a reduction in the degree of physical contact between the irritant and the skin. Good examples of raw materials that operate via this mechanism are thickeners that retard the rate at which irritants are be replenished at the skin/formulation interface.
Several methods have been used in measuring the irritation values. The examples of in vivo methods of measuring irritation and anti-irritating effects include Repeated Insult Patch Testing (RIPT) and Draize methods, both known to those skilled in the art. The examples of in vitro methods are Eyetex™ by InVitro International, and EpiDerm™ and EpiOcular™ by MatTek Corporation. Another method of measuring irritation was described by R. Goldemberg in Reduction of Topical Irritation, J. Soc. Cosmetic Chemists, 28, 667–679 (1977), which is incorporated by reference herein.
The art of reducing irritation has not been perfected and the need still exists for effective anti-irritants. For example, there exists a need for ingredients that reduce the irritation produced by surfactant-based cosmetic and/or personal care formulations. Anti-irritants which are easily compatible with the personal care formulations and/or which are able to contribute other advantageous properties such as such as stabilization, wetability, spreadability, viscosity, etc., are particularly desirable. It is especially desirable to find anti-irritants that are also able to contribute to a superior after-feel of the product and/or allow the formulation of a clear product.